This invention generally relates to receivers for digital data transmission. More specifically, the invention relates to FM broadcast digital data pagers using SCA (Subsidiary Communications Authorization) channels.
Pagers have typically used FSK (frequency-shift-keying) for digital data transmission. But BPSK (binary-phase-shift-keyed) modulation has many desirable advantages for digital data transmission including a reduced bandwidth requirement for a given data rate, minimal error rates under low signal-to-noise ratio conditions, and simple circuitry for generating the modulated signal. When coherent detection is used, BPSK also provides very reliable signal recovery in the presence of interference. However, BPSK modulation has not been used widely in paging systems because the acquisition and demodulation of the BPSK signal has required the use of more complex and expensive circuitry consuming an increased amount of power. In particular, the use of BPSK modulation in FM-SCA pagers is subject to signal acquisition and synchronization difficulties compounded by interference from the audio program material. Overcoming these disadvantages towards efficient use of BPSK modulation constitutes a significant improvement in digital data paging systems.